As per my understanding,Singletion Session Bean is instantiated once per application per class.
However, in the server.log I see that it is Instantiated(Created) twice in application (See message "INFO: *** SingletonSessionBeanA - Created" is displayed twice)
Please advise if my understanding is incorrect.

This is what I also noticed when I was preparing for the exam: the constructor of a Singleton is called twice (!). This is an implementation specific thing not mandated (or explained) by the specifications. The PostConstruct method is only called once luckily...